Watermark Category Images with Brand Logo

I’d like to add a watermark to each small image (but only in the category listing page) that is based on the manufacturer attribute. I don’t want to alter the small image for that product on other pages.

I’ve thought about setting a watermark for small images and overriding the image file, but that will add the watermark to all small images for that product (which might be shown on other pages).

Is there a somewhat easy way to do this without creating a custom module?

Mage_Catalog_Model_Product_Image::setWatermark